Motor fuel production process

ABSTRACT

HIGH AROMATIC CONTENT MOTOR FUEL IS PRODUCED FROM C5-C8+ NAPHTHA BY SEPARATING THE NAPHTHA INTO A C5-C6 CUT, A SEPARATE C7 CUT AND A C8+ CUT; CATALYTICALLY DEHYDROCYCLIZING THE C7 CUT; CATALYTICALLY REFORMING THE C8+ CUT; AND THEREAFTER COMBINING THE THREE FRACTIONS. IN PREFERRED MODES OF OPERATION, THE C7 CUT IS ALSO SUBJECTED TO CATALYTIC REFORMATION AND THE C5-C6 CUT IS ISOMERIZED BEFORE COMBINATION WITH THE OTHER HYDROCARBON FRACTIONS.

United States Patent O 3,776,837 MOTOR FUEL PRODUCTION PROCESS Frits M. Dautzenberg and Henk .I. Alkema, Amsterdam, Netherlands, assignors to Shell Oil Company, New York, N.Y. No Drawing. Filed Oct. 20, 1971, Ser. No. 191,088 Claims priority, applicatgriggtsherlands, Nov. 19, 1970,

Int. Cl. C10g 31/14, 35/06 US. Cl. 208-65 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention This invention relates to an improved process for preparing high aromatic content hydrocarbon mixtures useful as motor fuels from C C naphtha.

The prior art Gasoline range naphthas comprise blends of 5 to 8+ carbon atom paraflins and are major constituents of gasoline. These naphthas have the disadvantage as motor fuels of having low octane numbers.

The formation of aromatic compounds from naphthas is known to increase the overall octane number. A great variety of processes involving catalytic reforming have been developed to increase the aromatic content of naphthas. In some of these reforming processes, such as the process disclosed in US. 2,918,422, issued Dec. 22, 1959 to Evering et al., the naphtha is separated into two fractions which are separately treated and then recombined.

STATEMENT OF THE INVENTION It has now been found that the aromatic content of a C -C naphtha can be increased with improved efficiency when the naphtha is first fractionated into three fractions which are treated separately and thereafter blended. The three fractions and their separate treatments are (A) a C fraction which is catalytically dehydrocyclized and then optionally catalytically reformed, (B) a heavy (03 fraction which is catalytically reformed, and (C) a light (C -C fraction which optionally is hydrogenated and isomerized. This process has the advantages over prior processes of permitting the 0, fraction dehydrocyclization to be operated to maximize selectivity to aromatics without the usual risk of yield losses from C -C cracking. Thus, both gasoline range hydrocarbon yield and aromatic selectivity can be optimized.

DETAILED DESCRIPTION OF THE INVENTION The fractionation In accord with this invention a C C naphtha is first separated into three fractions (cuts). This separation is suitably carried out in distillation columns as is known in the art to give a fraction consisting entirely or substantially (at least 90%, preferably at least 95%) of C hydrocarbons, a heavy fraction containing primarily C hydrocarbons and a light fraction consisting essentially of C -C hydrocarbons.

3,776,837 Patented Dec. 4, 1973 The C fraction dehydrocyclization The C fraction is dehydrocyclized, that is, it is contacted with a catalyst which at elevated temperatures and in the presence of hydrogen causes parafiins having a chain of at least six carbon atoms to form into six carbon atom rings and thereafter causes these rings to dehydrogenate to aromatics. Very suitable catalysts for this reaction are nonacidic catalysts which contain on a nonacidic carrier at least one noble metal of Group VIII of the Periodic Table and at least one additional metal which has an electronegativity of from 1.6 to 2.0 and which belongs to the fifth or sixth periods of the Periodic Table. The Periodic Table referred to in this application is that found in the 43rd edition of the Handbook of Chemistry and Physics published by the Chemical Rubber Publishing Company.

The noble metals of Group VIII which may be present in the catalysts used for the C fraction dehydrocyclization include platinum, palladium, rhodium, ruthenium, iridium and osmium. If desired, two or more of these metals may be present. Platinum is a preferred noble metal. The quantity of noble metal is suitably from about 0.01 to about five percent by Weight, basis the entire catalyst, preferably from about 0.05 to about two percent by weight.

Metals found in the fifth and sixth periods which have electronegativities of from 1.6 to 2.0 and which are useful in these catalysts include silver, cadmium, mercury, indium, thallium, tin, lead, bismuth, molybdenum, tungsten, rhenium, and technetium. Electronegativity values for these metals are tabulated at page 78 of R. T. Sandersons textbook Inorganic Chemistry (1967 edition, Reinhold). Preferred among these metals are tin and bismuth, with tin being most preferred. Combinations of these metals may be used. The amount of these metals added to the dehydrocyclization catalysts is suitably up to about five percent by weight, preferably from about 0.05 to about 2.5 percent by weight, basis the entire catalyst.

The support employed in these catalysts is preferably a porous nonacidic alumina often very suitably containing a small amount, for example, up to about one percent by weight, of sodium or potassium. These catalysts and their preparation are described in detail in UK. patent application No. 39,408/69, filed Aug. 6, 1969.

The dehydrocyclization of the 0, fraction is preferably carried out at a temperature of from about 375 C. to about 650 C., a pressure of from about 0.1 to about ten kg./cm. a weight hourly space velocity of from about 0.1 to about 19, and a hydrogen to feed molar ratio of from about 0.5 to about five. Hydrogen should be added to stabilize the catalyst, but need not be pure. Hydrogencontaining reforming eflluent gas may be used, for example.

The C fraction reformation The 0 fraction is subjected to catalytic reformation, that is, it is contacted with a catalyst which, at elevated temperatures and in the presence of hydrogen, causes the dehydrogenation of 0 alkylcyclohexanes to alkylaromatics, the dehydroisomerization of C alkylcyclopentanes to alkylaromatics and the isomerization of paratfins and aromatics.

Suitable catalysts for this purpose are acidic noble metal catalysts such as platinum on an acidic alumina carrier. Such catalysts may contain more than one noble metal and additionally may contain other metals, preferably transition metals, such as rhenium, tungsten, tin, bismuth and the like, and halogens such as chlorine or fluorine. Catalysts of this type are available commercially.

Catalytic reformation of the C fraction is suitably carried out at temperatures of from about 400 to about 3 600 0., preferably from about 450 to about 550 C., pressures of from about ten to about fifty kg./cm. weight hourly space velocities of from about 0.5 to about ten, preferably from one to five, and a hydrogen to feed molar ratio of from five to fifteen.

It is often desirable to subject the C fraction after dehydrocyclization to catalytic reformation in order to dehydroisomerize ethylcyclopentanes or dimethylcyclopentanes present in the C7 fraction. These materials are effectively converted to aromatics by reformation. Dehydroisomerization of the dehydrocyclized 0, fraction may be carried out separately by a separate reforming operation, as described above, or by combining the dehydrocyclized C fraction with the C fraction prior to its reforming. It is preferred to reform the dehydrocyclized C fraction by mixing it with the C fraction and together passing them over the same reforming catalyst.

The C C fraction hydrogenation and isomerization Blending of the reformed C fraction and the dehydrocyclized and optionally reformed 0, fraction with the previously separated C -C fraction produces a useful high aromatic content motor fuel. An even higher octane product is achieved if the C -C fraction is isomerized before it is blended with the other fractions. This treatment may be carried out by contacting the C -C fraction with, for example, a hexafluoroantimony acid catalyst as described in British Pat. 981,311 or a platinum/mordenite catalyst as described in British Pat. 1,151,653. Treatment with a hexafluoroantimony acid catalyst is preferred.

If the C -C fraction is to be isomerized, it is desirable to carry out two prior preparatory steps to ensure the life of the isomerization catalyst. The C -C fraction typically contains benzene and most likely also contains sulfur compounds. Both benzene and sulfur compounds have adverse effects on the isomerization catalysts and should be removed. Benzene is most easily removed by hydrogenation using hydrogen and a Group VI or VIII catalyst such as an up to 65 percent by weight nickel on alumina or kieselguhr catalyst or a 0.1 to two percent by weight platinum on alumina catalyst.

Any sulfur present is typically present in the C -C fraction primarily as mercaptans. These materials may be removed from the fraction by oxidative conversion to nonvolatile disulfides followed by distillation overhead of the C -C fraction. This sulfur removal should be carried out prior to the benzene hydrogenation as the sulfur materials can harm the hydrogenation catalysts. The sulfur compound (mercaptan) oxidation may be simply eflFected by contacting the mercaptans with air or oxygen, preferably in the presence of a metal (especially copper) catalyst. Porous ion exchange resins containing from about five to about ten percent by weight of cupric copper are excellent mercaptan oxidation catalyst. This catalytic oxidation is carried out, in a preferred modification, prior to or during the initial naphtha fractionation. If a copper catalyst and oxygen (air) ar both present in the distillation column used to separate overhead the C -C fraction, any mercaptans present will be oxidized to disulfides and thus not taken overhead with the C -C fraction, rather going into the C or C fractions where they will have no adverse effect.

The blending Following the above-described treatments, the C -C fraction, the C fraction, and the C fraction are blended together to give the final high aromatic content hydrocarbon motor fuel. It is not essential to the practice of this invention that these fractions be blended in exactly the proportions they were separated. Amounts of one or more of these fractions may be omitted from the final blend if desired. Generally, however, essentially all of each fraction is blended.

The following examples are provided to illustrate the process of this invention. They are not intended to be construed as limiting the scope of the invention.

4 EXAMPLE I A C -C naphtha was split by distillation into a C C fraction, a 0; fraction and a C fraction. The distillation column contained a commercial porous ion exchanger (Amberlyst 15) on which 7.8 percent weight copper in the form of cupric ions had been deposited. During the distillation a small amount of air was added to the feed in order to oxidize the mercaptans present in the naphtha feed to disulfides. The compositions of the C and C fractions are given in Table I.

The 0, fraction obtained was dehydrocyclized in a reactor I with the aid of a nonacidic catalyst which contained platinum and tin on alumina as carrier, and the product obtained was dehydroisomerized in a reactor II with the aid of a catalyst which contained platinum on acidic alumina as carrier. In three adiabatic reactors IIIA, IIIB and IIIC, which were connected in series, the C fraction was reformed with the aid of a catalyst which contained platinum on acidic alumina as carrier.

The products obtained from reactors II and III were combined. Table I gives the conditions in the reactors (pressures, temperatures, hydrogen/feed ratios, weight hourly space velocities), the yields of components which can be used as gasoline components, that is, the percentage of compounds with five or more carbon atoms, and the percentages of paratfins, naphthenes and aromatics therein (all percentages calculated on the quantity of feed), the content of aromatics in percentages of the total quantity of compounds with five or more carbon atoms, the ring retention and the selectivity.

TABLE I Reactor- Conditions:

Weight hourly space velocity. Pressure, kg./em. Hydrogen/hydrocarbon molar ratio Temperature, 0 5 Yield percent weight:

.a E NU! mi Hydrocarbons with ve or more carbon atoms (05*) 05+ paraifine Ring retention Selectivity 3 Aromatics in 05*, percent weight- 1 Average temperature of 3 reactors.

percent weight of ring structures in productXlOO. Ring retention percent weight of ring structures in feed quantity of six-membered rings formed 8 Selectivity quantity of converted paraflius plus cyclopentanesXlOO;

EXAMPLE II TABLE II Reactor.

Conditions:

Weight hourly space velocity Pressure, kgJcrn. Hydrogen/hydrocarbon molar r Temperature, C Yiellt iffpercent weight:

C1-C4 paraffins Hydggcgrbons with live or more carbon atoms 5 05+ paraffins- 05+ naphthenes. 05 aromatics. Ring retention Selectivity 3 Aromatics in 05+, percent w ht 1 3 8 See footnotes bottom of Table I.

COMPARATIVE EXPERIMENT A TABLE III II Reacton- A, B,

Conditions:

Weight hourl space velocity Pressure, kg. cm. Hydrogen/hydrocarbon molar ratio Temperature, C Yiellz il, percent weight:

C1-C4 paraffins Hydrocarbons with five or more carbon atoms 0 paraflins- 0 nanhthenes 05+ aromatics- Ring retention Selectivity Aromatics in 05+, percent weight 13 3 See footnotes bottom of Table I.

Comparison of the results of Example I and the Comparative Experiment A shows that at almost equal contents of aromatics in 0 the yield obtained according to the process of the invention is considerably higher than that obtained according to the conventional process. Comparison of the results of Example II and the Comparative Experiment A shows that at almost equal yields a much higher content of aromatics in the product (which is an improvement of the quality) is attained with the process according to the invention.

We claim as our invention:

1. A process for converting a C to C naphtha into a high aromatic content hydrocarbon motor fuel which comprises:

(a) separating the naphtha into a C to C fraction, a

C consisting of at least 90% C hydrocarbons, and a C fraction;

(b) subjecting the 0; fraction to catalytic dehydrocyclization;

(c) subjecting the 0 fraction to catalytic reformation; and

(d) admixing C to C fraction, dehydrocyclized C1 fraction and reformed C fraction.

2. The process in accordance with claim 1 wherein the dehydrocyclized C fraction is subjected to catalytic reformation prior to being admixed with the C to C fraction and the reformed C fraction.

3. The process in accordance with claim 1 wherein the C to C fraction is freed of any sulfur contaminants and subjected to hydrogenation and isomerization before it is admixed with the dehydrocyclized C fraction and the reformed C fraction.

4. The process in accordance with claim 3 wherein the dchydrocyclized C fraction is subjected to catalytic reformation prior to being admixed with the hydrogenated and isomerized C to C fraction and the reformed 0 fraction.

5. A process for converting a C to C naphtha into a high aromatic content hydrocarbon motor fuel which comprises:

(a) separating the naphtha into a C to C fraction, a

C fraction consisting of at least 90% C7 hydrocarbons, and a C fraction;

(b) subjecting the 0; fraction to catalytic dehydrocyclization;

(c) admixing the dehydrocyclized C fraction with the C fraction and subjecting the admixture to catalytic reformation; and

(d) admixing C to C fraction and reformed C and 0 fractions.

6. The process in accordance with claim 5 wherein the C to C fraction is freed of any sulfur contaminants and subjected to hydrogenation and isomerization before it is admixed with the dehydrocyclized and reformed 0; fraction and the reformed 0 fraction.

References Cited UNITED STATES PATENTS 3,384,571 5/1968 Engel 20879 3,018,244 1/ 1962 Stanford et a1 20879 2,890,994 6/1959 Donnell et a1 208 3,000,810 9/ 1961 Christensen et al. 20879 2,944,001 7 1960 Kimberlin et al. 20880 3,002,917 10/1961 Hamilton 20879 3,003,949 10/ 1961 Hamilton 20879 2,938,936 5/1960 Belden 260--683.68

DELBERT E. GANTZ, Primary Examiner G. E. SCHMITKONS, Assistant Examiner US. Cl. X.R. 

